Cutting tools having a pin-type retaining means are known in the art. For example, Kelm, U.S. Pat. Nos. 3,341,920 and 3,341,923 disclose pin-type retaining means insertable into an axial hole of the cutting tool, wherein when the pin is driven axially into the hole, the pin forces the cutting insert radially against the supporting shoulder of the tool body to thereby lock the cutting insert in place.
As the threads of the pin engage the corresponding grooves of the tool body, contact is made between the central tapered portion of the pin and the corresponding tapered portion of the axial hole in the tool body. As a result, the pin is forced laterally toward the shoulder of the recess against which the cutting insert rests providing a firm lock of the cutting insert against the shoulder.
More specifically as shown in FIGS. 2 and 3 of U.S. Pat. No. 3,341,920, the portion of the axial hole adjacent the base of the recess is tapered inwardly from the base of the recess to form a conical portion having a central axis identified by the line A--A. The remaining threaded portion of the axial hole in the recess of the tool body is cylindrical and has a central axis B--B offset from the axis A--A of the conical portion of the hole. The axis A--A is offset from the axis B--B in the direction toward the supporting shoulder of the shank. As a result, a significant force is applied against the cutting insert by the pin to thereby lock the same against the supporting shoulder U.S. Pat. Nos. 3,341,920 and 3,941,923 are incorporated herein by reference.
Such retention pins also have an axial hole in the bottom threaded portion of the pin extending upward toward the tapered section of the pin. The axial hole has grooves which mate with a drive means such as a hex wrench to provide a greater locking force at the bottom of the pin
These prior art devices are particularly suited for so-called lay-down type cutting inserts. However, such devices do not satisfactorily inhibit movement during cutting operations when on-edge cutting inserts are employed This is because the retention force generated by the pin is directed primarily radially in the direction of the shoulder of the recess and the only axial force is that due to the friction engagement of the cutting insert against the locking shoulders. The cutting forces generated in the axial direction of the locking pin may exceed the frictional force thereby resulting in movement of the cutting insert which can lead to tool failure
To overcome the problems with on-edge type of cutting inserts, tool clamps have been used which apply a clamping force against the top surface of the cutting insert substantially perpendicular to the cutting edge to maintain the same in the locked position The clamp is used in conjunction with pin-type retaining means described previously to provide a locking force exceeding that of the frictional force.
The use of a clamp in conjunction with pin-type retaining means has three primary disadvantages. First, the clamp is bulky and can prevent or inhibit access to certain workpieces and therefore, cannot be used in some machining operations.
Second, additional time and effort must be expended to lock and unlock the clamp and the cutting insert. A third disadvantage is that the clamp and those tools which are used to lock and unlock the clamp add significantly to the cost of the cutting tool. These disadvantages have made the use of clamps with pin-type retaining means of limited value for on-edge cutting tools.
The present invention overcomes the disadvantages of the aforementioned prior pin-type retaining means by employing a double pin retention assembly which provides a locking force not only radially towards the supporting shoulder but also axially to provide an axial locking force which greatly exceeds the frictional force between the cutting insert and the recess. Furthermore, the double pin retention assembly of the present invention eliminates the need for cumbersome and expensive tool clamps.
It is therefore an object of the present invention to provide a cutting tool having a double pin-type retaining means which provides both a radial and axial locking force to more securely retain the cutting insert in the pocket of the cutting tool.
It is a further object of the invention to provide a cutting tool having a double pin-type retaining means especially suited for locking an on-edge cutting insert so that movement during cutting operations is substantially eliminated and tool failure is significantly reduced.